Welcome to the Forum!!
That is truly a tough situation, but at the end of the day you are right, she is 28 yrs old, it's sink or swim time, she is an adult, you can't make the decisions anymore of how she chooses to run her life, only she can turn things around, sure you can give her advice and words of discouragement towards her actions but only she can turn things around, I fear though for her unborn child unless things really do change.
For you though, have you sought some support? there are groups and places you as a family member of an addict can receive support to get you through, to talk to other people in a similar situation, that may be a way forward!!